Mitosis and the Cell cycle

The reading guide is here

A brief introduction. Watch this before getting further into the weeds.

This video covers how mitosis happens. As you learn about mitosis, the main thing you should focus on is how the cell ensures that each of the daughter cells is identical.

This video looks at how the cell cycle is regulated, and how cancer starts when that regulation doesn’t work properly.

Optional: You can explore more about cell cycle regulation here
Modeling Mitosis. Doing this exercise will help you to understand how chromosomes move during mitosis. It’s really easy to watch it happen, it’s much harder to actually know how it happens. It should take about 10 minutes to do.

Modeling mitosis

What you need:

4 knives. Two of them should be identical, and the other two should be different from the first two, but identical with each other. For example, you might have 2 metal knives and 2 plastic knives.
4 forks. Two of them should be identical, and the other two should be different from the first two, but identical with each other. For example, you might have 2 metal forks and 2 plastic forks.

What do do:

Lay out 1 plastic knife, 1 metal knife, 1 plastic fork, and 1 metal fork on your table. These represent your 2 pairs of homologous chromosomes. You inherited the metal utensils from your mother and the plastic utensils from your father. The knife represents chromosome 1 and the forks represent chromosome 2.
The homologous pairs are similar, but not identical. They have the same genes on them, in the same order. Knives are knives, but they are slightly different (metal vs. plastic). The genes on them have been accumulating mutations in your mother’s lineage and a different set of mutations in your father’s lineage, so they are not identical.
Your cell is now in G₁ phase.
Your cell advances through S phase. The DNA duplicates
Place the second copy of each utensil next to its identical copy. These are sister chromatids. They are identical because they are the result of the chromosomes being copied during S-phase.
Your cell is now in G₂ phase and ready to enter mitosis.
As your cell goes through mitosis, you can identify all of the different events that happen at each stage – such as the centrosomes separating, the nuclear envelope disintegrating, etc. For this exercise, however, the important thing is to focus on where the chromosomes move.
Your chromosomes should still be paired up as sister chromatids. The plastic fork should be with the plastic fork, and it should NOT be associated with the metal fork.
By Metaphase, your chromosomes should all be lined up on the metaphase plate. You can place all 4 pairs in a line, but don’t separate the sister chromatids.
By Metaphase, spindle fibers are attached to all kinetochores. This is a checkpoint on the cell cycle that can’t be passed unless the kinetochores are all attached.
In anaphase, separate the sister chromatids to one side or the other as they move along the microtubules.
In telophase, the nuclear envelope reforms around each set of chromosomes.
Your ‘cell’ should now have 2 clusters of utensils. On one side, there should be a metal fork, a metal knife, a plastic fork, and a plastic knife.
Cytokinesis divides the cytoplasm so you should now have 2 full, distinct cells.
Check to make sure that the chromosome content of each cell is correct. Each cell should be identical to one another and to the state of the cell way back in G₁ phase. This shows you how mitosis is a sort of cellular photocopier.
Do this exercise again (it’ll take about 1 minute the second time) to make sure you fully understand how the chromosomes move.